The premature and mistaken announcement of Florida's presidential winner by US television networks on election night was "unconscionable," said the Vatican's top expert in media ethics.

Not only did the early calls violate ethical requirements for accuracy, but they may have discouraged potential voters in the state from casting ballots, Archbishop John P. Foley, an American who is president of the Pontifical Council for Social Communications, told Catholic News Service.

"To base an alleged winner or loser on the basis of exit polls or of incomplete returns I think is unconscionable, especially when such an announcement can have an effect in areas where polls remain open," he said.